Devices for detecting a line of sight or gaze point of a test subject in a noncontact manner have conventionally been regarded as important in the field of human interactions. High-precision line of sight detection techniques, if put into practice, can be employed for various uses such as monitoring drivers, inspecting degrees of interest in products, and aiding severely disabled people to input data to personal computers, for example.
Line of sight detection methods disclosed in the following Patent Literatures 1 and 2 make a test subject gaze at both a camera whose position has been known and one point whose position has been known on a display screen, so as to correct a function for calculating a line of sight direction of the test subject from the distance |r| between the center of a pupil and a corneal reflection point, and detect the line of sight direction by using thus corrected function. Such a line of sight detection method can detect a line of sight highly accurately even when the head of the test subject moves. The line of sight detection method disclosed in the following Patent Literature 3 is a method for detecting lines of sight of both eyes at the same time by using two cameras. It is also necessary for this method to make the test subject see a specified point in order to calibrate results of the line of sight detection.